In general, the invention relates to xe2x80x9charvestingxe2x80x9d water from the atmosphere.
Military expeditionary activity and other field deployments such as for disaster relief requires considerable amounts of fresh water. Water, for instance, constitutes about 40% of the required logistics support. This situation imposes considerable logistical xe2x80x9cdragxe2x80x9d in the supply system. The requirement to deliver water to forward deployments has been known to delay delivery of other requirements such as fuel, ammunition, and other military supplies, which affects timeliness and possibly even success of the mission. Likewise, persons traveling in areas where water is scarce or of dubious quality often must settle for treated water that is medically acceptable but unpalatable. Remote location water treatment procedures are often difficult to implement properly.
The U.S. Department of Defense recommends 1-3 gallons of water per soldier per day, but accepts 1 gal/day as a minimum in constrained circumstances. On a daily basis, a 2-3 quart water deficit leads to a 50% degradation in performance, and a 4-quart deficit renders the soldier incapacitated after as few as three days. On average, a soldier loses 600 mL of water per day via evaporation from the skin, 350 mL via respiration, 15 mL via urine, but gains 350 mL via metabolism (water of combustion).
Ideally, in a maneuver situation, a group of soldiers would be supplied with the equivalent of 3-7 days worth of water without re-supply. Current doctrine allows for 6.6 gallons of water per day for all uses (imbibing, washing, cooking, laundry, etc), but a xe2x80x9cfully developedxe2x80x9d theater requires 15.6 gallons of water/soldier/day. Thus, an Army brigade will use 106 tons (English units) of water per day (1 gallon of water weights 8.3 lbs).
Providing water for forward deployments of military expeditionary activity or disaster relief situations has typically required either xe2x80x9ctankering inxe2x80x9d already treated water or finding water near the locality where the water is required and treating it on site. In the former case, shortening the distance over which the potable water must be brought is the first order solution to water supply. Deployable desalination and water purification equipment considerably shortens the logistical supply chain and provides a major saving of logistical transport capacity. Current Army water treatment procedure for producing potable water from saline or brackish water is to pretreat (e.g., filter) the water, followed by reverse osmosis, deionization and fine filtering and by chlorination. This water supply protocol is energy- and equipment-intensive, and water supply operations are easily disrupted in a conflict or high stress situation.
With respect to the latter procedure, in the operational area (OPAREA), deployed personnel must find and treat water. A conventional source (river, puddle, well, etc.) is usually available, but this found water usually must be treated to bring it to acceptable, safe drinking water standards. In practice, these standards may not be reached, and this situation is usually reflected in the declining health of field personnel. Thus, better methods for obtaining water are needed, particularly in arid and semi-arid areas where water is very scarce and often highly brackish with dissolved solids.
According to one embodiment of the invention, a self-contained apparatus for harvesting water from the atmosphere converts sunlight to electrical energy via photovoltaic systems; stores that electricity; and then uses the electricity to provide modest refrigeration on the panel face to foster condensation of atmospheric moisture. These essentially passive condensation panels can be fabricated as structural elements of existing equipment, such as the panel sides of ambulances and some portable buildings, or provided as flexible, collapsible panels that can be hung from frames or existing points of opportunity such as trees.
The present invention provides a new method and apparatus for harvesting atmospheric moisture using a light-weight, self-contained, xe2x80x9cpassivexe2x80x9d system for harvesting water from atmospheric moisture at those times of the diurnal cycle when relative humidity is at or close to 100%. Although the air may contain lower percentages of water during the heat of the day, most local air masses carry considerable volumes of air at near relative humidity for several hours each early morning. At these times, accelerated collection of water may be carried out using water harvesting panels according to the invention. Although it is believed that the invention will not provide all required water in all circumstances, it is believed that the invention will provide water in significant quantities to reduce substantially the amount of water that presently has to be transported, usually in hazardous conditions and at great cost. This reduced water transport requirement will be reflected by reduced costs and increased operational capability as the operational elements and personnel freed up can be used for more direct, militarily relevant materials and supplies.
According to the invention, a panel or surface is cooled in the presence of air containing significant amounts of moisture. Heat absorption on the surface of the panel, which is maintained at a temperature that is below the ambient temperature but above a heat-absorbing level that would cause freezing of condensing water, promotes and accelerates condensation on the surface. The surface on which the condensation takes place is preferably coated with suitable hydrophilic and hydrophobic materials disposed so as to promote the condensation and flow and collection of condensing water along channelways. The nature of the surface may be altered electrically, chemically, or by other means to allow it to promote condensation of water, and its subsequent gathering.
Panels can be employed in fixed shape form or in collapsible and flexible form. Panels may replace existing structural parts of vehicles or equipment panels such as the sides of ambulances and other vehicles and some portable buildings. They may be used as part of prepared camouflage, as they must be non-reflective and virtually noiseless. Deployed within tents or buildings, the units will be capable of recovering respired water vapor.
In some types of this apparatus, there may be few or no moving parts. Ideally, all components are solid state and hardened, although micro-refrigeration circulation systems or embedded heat/refrigeration systems may be employed.
The invention will now be described in greater detail in connection with the drawing, in which:
FIG. 1 is a generalized perspective view of a water harvesting panel according to the invention.